The invention relates to an axial adjusting device having two discs which are rotatable relative to one another and coaxially supported relative to one another. Between the two discs, balls are guided in pairs of ball grooves in the discs. The depth of the pairs of ball grooves is variable across the circumference of the discs. One of the discs is axially supported and one is axially displaceable against resilient returning forces of the spring mechanism. At least one of the discs can be driven rotatably by a motor via a gear drive.
In this embodiment, a rotatingly driven disc can, at the same time, constitute the axially displaceable disc, but this is an exception. Normally, the supported disc is rotatingly driven and the axially displaceable disc which, in turn, is supported thereon via the balls, is held in a rotationally fast way.
For the purpose of actuating the axial adjusting device, the motor is driven in a first direction of rotation, with the at least one disc coupled to the motor via reduction stages being rotated and with the axially displaceable disc which, in turn, supports itself on the axially supported disc, being axially displaced against resilient returning forces of the spring mechanism.
As a result of the discs rotating relative to one another, the balls, which rest in pairs of ball grooves against end positions and which, at the same time, are positioned therein in the deepest groove portions, run towards shallower groove portions. As a result, the discs are pushed away from one another.
If the motor is driven in the opposite direction or is switched so as to be current-free, the displaceable disc is pushed back by the resilient returning forces applied thereto by the spring means and the at least one rotatably drivable disc is rotated back actively by the motor or as a result of the effect of the balls in the ball grooves until the balls in their pairs of ball grooves stop against the end positions simultaneously. As a result of the balls stopping in this way against the ends of the ball grooves, the rotating masses of this system, i.e., the rotatable one of the discs, the gears of the gear drive and the shaft of the motor with the rotor mass, are stopped abruptly.
Even elastic deformation of the motor shaft caused by the pulse generated as a result of the rotating masses stopping abruptly, can lead to tooth fracture at the pinion or at the set of gears. This is because, when the motor shaft is bent, the points of force application in the toothings move outwardly, resulting in loads acting on the pinion or the set of gears exceeding the design loads.